[data grid] Use multiple tabs instead of package for mock data set

[joserodolfofreitas]

Summary

To enhance transparency and devEx, I propose replacing the current dataset mocker package (x-data-grid-generator) with a more direct, user-friendly approach: we leverage the new "multi-tabs" feature of our docs-infra to embed the code snippets directly within the docs in a separate tab, so we don't pollute the main aspects of the code.

This will allow users to view, copy, and paste relevant code easily. The change aims to simplify the user experience by making code samples more accessible and reducing dependencies on external packages.

Motivation

• Often users can't find the examples they are looking for within our docs (Like renderCountry and renderRating, which are hidden behind the package)
• useDemoData is top1 of searches without a hit on our docs

Search keywords:

[joserodolfofreitas]

The docs-infra team is working on a way to reuse tabs/resources in different examples.
We should wait until this is ready to replace useDemoData.